Explore Geology
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Ice Age

National Scientific Reserve


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park geology subheading
photo of vegetation and geology
Ice Age National Scientific Preserve, Wisconsin


Each year we see the northern United States altered by the cycle of the seasons, but this has not always been so. During a recent geologic period this land did not undergo seasonal changes. Great areas lay under thick layers of ice. For more than a million years, in at least four major periods of glacial advances, ice covered much of Canada and the northern United States. These four glacial stages, Nebraskan, Kansan, Illinoian, and Wisconsinan, are named for their most southerly advances.

The Wisconsinan stage covered much of the northern United States from the Atlantic coast to the Rocky Mountains as recently as 12,000 years ago. Nowhere is the evidence of the glaciers better preserved than across Wisconsin. As you drive around the State you can see many lakes and ponds, forested hills and ridges, and gently rolling farmlands that remind us of the glacier's visit. The Ice Age National Scientific Reserve was established in 1971 to preserve select glacial landforms and landscapes. The Reserve, part of the National Park System, consists of nine units administered by the Wisconsin Department of Natural Resources.

In southeastern Wisconsin, certain distinctively shaped hills and ridges occur repeatedly and in patterns that rule out the possibility of random distribution. These recurring landforms are mementos of the Wisconsinan glaciation, the most recent major episode in Earth's geological history. Because each landform was shaped by the ice sheet under a special set of conditions, it is fairly easy for observers of glacial geology to recognize them. And with the help of this information, you should be able to recognize them too. Besides that, you will see much of Wisconsin's great scenic beauty in these interesting glacial landforms. The great sequence of events that did so much to shape the northern half of North America and Europe spanned perhaps 1.5 million years. The Wisconsinan stage, the latest series of glacial advances and retreats began possibly 70,000 years ago and ended only 10,000 years ago. In fact, we can't even be certain that we are not in fact still in the Ice Age and merely enjoying a warm period between two glacial advances.

This knowledge, strangely, is only about a century old. Until the mid-19th century no one could account satisfactorily for drumlins, kames, eskers, kettles, moraines, and other such phenomena. It was the great Swiss naturalist Louis Agassiz who announced to a skeptical world the bold new theory of continental glaciation. Today it is universally accepted and is the focus of a whole branch of geologic investigation. The areas protected as the Ice Age National Scientific Reserve give you a good "on-the-ground" introduction to Ice Age geology.

Variations in topography and snowfall caused the massive ice sheet to move across the land at an uneven pace. The glaciers moved easily down river valleys and drainages, but massive hills slowed their movement. Higher upland areas caused the ice sheet to separate into tongues or lobes of ice moving outward from the main mass. Four major lobes of the Wisconsinan Glacier are recognized across the State:

  • Superior,
  • Chippewa,
  • Green Bay, and
  • Lake Michigan lobes.

We can only speculate about what Wisconsin looked like before the glaciers moved across the land. Undoubtedly, much of it was well-drained land like the southwestern portion of Wisconsin, an area so virtually untouched by glaciers that it is known today as the Driftless Area. As glacial ice advanced southward, hills and bluffs were often sheared off right down to bedrock. As the glacial front retreated, however, glacial debris suspended within the ice was deposited, filling depressions and leaving undrained, rolling lands. This layer of debris, varying from a few centimeters to a hundred meters or more, is the legacy of the glaciers.

The glaciers did not advance and retreat in one continuous movement. During a period of thousands of years the glacial ice moved slowly forward, stopped, retreated, and moved forward again. Suspended material would be deposited at the glacier's outer edge as the front melted and slowed. During periods of glacial advance much of this same material was lined and pushed into ridges or moraines. Materials were deposited at the leading edge of the ice sheets, forming end moraines, bands of hills marking the farthest points of the glacial advance across the State. Although the end moraine is no longer a continuous band of hills because of erosion, it is useful for studying glacial movements. Many of these landforms remain. Some were destroyed when the ice or water quickly eroded them. Other landforms have been destroyed as people removed the commercially valuable water-sorted sands and gravels that they contain.

Huge lakes were formed when the glaciers, with the bulk of their ice and deposits, blocked natural drainages. As the glaciers retreated northward many of these lakes drained, leaving broad flat lake beds that are now rich agricultural lands. Large marshes providing rich habitat for birds and other wildlife have developed in other old lake beds. Thousands of years of gradually warming climate forced the glaciers to retreat to northern latitudes. Plant and animal life driven southward by the glacial advance again began moving northward. Today, relict populations of plants associated with cooler northern climates persist in some deep gorges and valleys.

As plants and animals again reclaimed the land, nomadic man arrived. Small groups followed the game and foraged for plants. Over the years their numbers grew and tribes evolved. The extensive waterways left by the glaciers provided relatively easy transportation routes. The wetlands also provided homes for fish, fowl, and fur-bearing animals, a combination that attracted early explorers. The first permanent settlements were located along waterways. Forests spread across the land, and soon timber was harvested and shipped east via the waterways. The relatively flat land left by the glaciers was fertile and readily adapted to farming. Soon much of Wisconsin became farmland. Today, recreationists enjoy the rich glacial legacy of waterways and wetlands.

The Ice Age Shapes the Landscape
The two continental ice sheets that exist today— the Antarctic and the Greenland—suggest how awesome the Ice Age was. Two-thirds of all freshwater lies locked in the Antarctic sheet, which is, at its thickest, more than 4 kilometers (2.5 miles) deep.

Here in Wisconsin, the Earth's crust has rebounded 50 meters (160 feet) since the Ice Age glaciers receded. Rebound is subtle—1.3 centimeters (0.5 inch) per year—but the land features that glaciers leave behind are easy to spot. Moving slowly, glaciers nevertheless attacked the land with violence and power, grinding bedrock into fine powder. Then, once released, the staggering torrents of meltwater tore across the landscape, carving the gorge known as the Dalles of the St. Croix River. The waters' sustained force is evident in potholes abraded into bedrock. But most apparent on the Wisconsin landscape are features resulting from stagnant ice conditions and from deposition.

When the forward movement of glaciers reached equilibrium with meltback, stagnant ice resulted. Conical hills, called kames grew as debris washed through holes in the ice. Visualize kames as reverse funnels. As stream tunnels beneath glaciers filled up with debris, eskers formed. Eskers look like inverted streams winding across todays landscape. Depressions in the ground known as kettles, formed as stranded ice blocks melted and the debris covering them subsided. This melting process could take thousands of years. Some kettles are simple bowl-shaped depressions, but others are now bogs, marshes, or lakes.

Features deposited by the ice itself—not by meltwater—include ground and end moraines, drumlins, and erratics. The materials that compose them had not been sorted by the action of moving water. Ground moraines were deposited under moving ice, or were just let down like a carpet as stagnant ice melted. End moraines represent glacial dumps at the edge of moving ice and trend perpendicular to the glacier's direction of flow. There are three types of end moraine. Terminal moraines are the outermost end moraines of a glacier's advance, marking where it terminated. Recessional moraines are those left by retreating ice. Interlobate moraines are built between lobes of ice. Erratics are rocks carried from a distance in or on the ice. If you can keep all that straight, you're on your way to becoming a geologist!

Drumlins look like the upside-down bowls of teaspoons, or halves of teardrops. Their formation is not well understood. They were built up in layers beneath moving glaciers and usually occur in groups—sometimes in hundreds— behind the end moraines. A drumlin's long axis parallels the glacier's direction of flow.

Continental Glaciation
To understand the changes continental glacial ice sheets brought, you must grasp their magnitude. Over thousands of years the cold of arctic climates crept southward. Falling snow did not melt but accumulated year after year. Under pressure of its own weight, snow was changed to ice. In time an ice sheet more than 1,600 meters (1 mile) thick resulted. Its mass produced pressures causing it to spread.

Year by year and meter by meter, it moved across the land, engulfing soil and rock and incorporated them into its mass. Trillions of tons of materials, lifted, ground, and mixed together in glacial ice, were carried southward. Over the Ice Age's millions of years the land was leveled and the Earth's surface depressed by the ice sheets' weight. A small change in our preent annual temperature - a 5°C (9°F) drop - could renew such snow buildup.

park maps subheading

The General park map is available here.

For information about topographic maps, geologic maps, and geologic data sets, please see the geologic maps page.

photo album subheading

A geology photo album has not been prepared for this park.

For information on other photo collections featuring National Park geology, please see the Image Sources page.

books, videos, cds subheading

Currently, we do not have a listing for a park-specific geoscience book. A variety of books about the park can be found here.

Please visit the Geology Books and Media webpage for additional sources such as text books, theme books, CD ROMs, and technical reports.

Parks and Plates: The Geology of Our National Parks, Monuments & Seashores.
Lillie, Robert J., 2005.
W.W. Norton and Company.
ISBN 0-393-92407-6
9" x 10.75", paperback, 550 pages, full color throughout

The spectacular geology in our national parks provides the answers to many questions about the Earth. The answers can be appreciated through plate tectonics, an exciting way to understand the ongoing natural processes that sculpt our landscape. Parks and Plates is a visual and scientific voyage of discovery!

Ordering from your National Park Cooperative Associations' bookstores helps to support programs in the parks. Please visit the bookstore locator for park books and much more.

geologic research subheading


For information about permits that are required for conducting geologic research activities in National Parks, see the Permits Information page.

The NPS maintains a searchable data base of research needs that have been identified by parks.

A bibliography of geologic references is being prepared for each park through the Geologic Resources Evaluation Program (GRE). Please see the GRE website for more information and contacts.

selected links subheading

NPS Geology and Soils Partners

NRCS logoAssociation of American State Geologists
NRCS logoGeological Society of America
NRCS logoNatural Resource Conservation Service - Soils
USGS logo U.S. Geological Survey

teacher feature subheading

Currently, we do not have a listing for any park-specific geology education programs or activities.

General information about the park's education and intrepretive programs is available on the park's education webpage.

For resources and information on teaching geology using National Park examples, see the Students & Teachers pages.
updated on 01/04/2005  I   http://www.nature.nps.gov/geology/parks/icag/index.cfm   I  Email: Webmaster
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